What was found
DURING APP WHEN FLAPS 2 SELECTED L/E FLAP TRANS LIGHT STAYED ILLUM AND 4 SLAT SHOWED UNSAFE YELLOW ON OVHD PANEL FLAPS WERE SELECTED TO 5 AND ALL WENT GREEN AND SHOWED SAFE. ABOUT 5 SECS LATER L/E FLAP TRANS LIGHT REILLUM AND 4 SLAT SHOWED UNSAFE AGAIN. FLAPS WERE SEL TO 10 AND ALL WENT SAFE AND GREEN FOR REST OF APP AND ALL FLAP SETTINGS HIGHER THAN 5. WHEN 4 SLAT SHOWED UNSAFE CO PILOT VISUALLY COULD SEE 4 FLAP UP WHEN OTHERS WERE DOWN. REMOVED AND REPLACED NR 4 SLAT ACT PER MM. INSP R/INSTALL OF SLAT ACT PER MM RII C/W 655177.